Coating method and coated devices

ABSTRACT

Surface coating method for deposition of a chemically bonded ceramic coating on a substrate, includes the steps of preparing a curable coating slurry, depositing a coating of the slurry on at least a section of the substrate surface, and hardening the slurry. The step of preparing a curable coating slurry includes mixing calcium aluminate powder with water and at least one water-reducing-agent, such that a water-to-cement ratio in the range of 0.1 to 0.9 is achieved.

FIELD OF THE INVENTION

[0001] The present invention relates to a method for deposition ofceramic coatings, a biocompatible surface coating and devices coatedwith said biocompatible surface coating, and in particular to a methodfor deposition of ceramic coatings having a high degree ofbiocompatibility and medical devices for implantation, comprising asubstrate that is coated with such a biocompatible ceramic layer.

BACKGROUND OF THE INVENTION

[0002] Surface Coating Techniques

[0003] A vast variety of materials can be deposited as thin films orcoatings. This invention particularly focuses on ceramic coatings.Ceramic coatings are often used for properties like, hardness, friction,corrosion resistance, and biocompatibility.

[0004] The most established techniques for depositing ceramic ofcoatings are CVD (Chemical Vapor Deposition), PVD (Physical VaporDeposition), electrolytic deposition, and thermal spray deposition.Furthermore, there are numerous subgroups within each depositiontechnique.

[0005] CVD is a high temperature process (typically 800° C.-1000° C.),wherein a chemical reaction occurring between the surface of a substrateand a gas that is flooded over the surface, generates a surface film onthe substrate. The technique is mainly used for deposition of metalcarbides, -nitrides or -oxides upon temperature resistant substrates,such as hard metal. The thickness of the deposited films may be in therange from nanometers to micrometers.

[0006] PVD is based on physical processes, most often plasma techniques,and may be used at lower temperatures than CVD, typically 300° C.-500°C. at the substrate surface. Contrary to CVD, PVD processes are line ofsight processes, which imply that it is not possible to deposit filmsaround corners, inside tubes, etc. PVD may be used for deposition ofpure metals and a large number of chemical compounds. PVD methods arecommonly used for deposition on temperature sensitive substrates, suchas steels, aluminum and even plastic materials. The coating thicknessesare of the same order of magnitude as for CVD processes.

[0007] Thermal spray deposition includes techniques based on gas flame,electric arc and gas plasma, all of which involve extremely hightemperatures. The melting zone may reach temperatures in the order of 10000° C. This set requirements on the temperature properties of bothsubstrate and coating materials. Thermal spraying may be used fordeposition of a number of metallic and ceramic materials. In general,the deposited films are thicker than for PVD and CVD, in the range of100 micrometers to a few millimeters.

[0008] A disadvantage with existing techniques for deposition of ceramicfilms is the elevated temperatures required in the process. Therefore,the most preferred of the above methods is often PVD, which may be usedfor deposition around 300° C. Another disadvantage is that said methodsrequire advanced deposition equipment, especially CVD and PVD, for whichgas-tight vacuum-arrangements are needed.

[0009] The main disadvantage with thermal spray deposition is thetemperatures of the melting zone. Also the cooling rate of the depositedmaterial is extremely high. Cooling from typically 10 000° C. to roomtemperature in a few microseconds, implies that possibilities to controlthe micro-structure of the coating are very limited. Phase-composition,chemical composition, porosity and surface structure cannot beaccurately regulated.

[0010] Biocompatible Materials

[0011] As for bioceramics, hydroxyapatites, or other calcium phosphates,are of particular interest. Hydroxyapatite is osseo-compatible, sincebone tissue regenerates excellently against this ceramic. The materialseems to be capable of forming a direct bond with natural bone. Onereason for this may be that human bone tissue is composed of about ⅔ ofhydroxyapatite.

[0012] As pure bulk material hydroxyapatites and other calciumphosphates have poor mechanical properties. Hydroxyapatite is thereforeoften used as a coating material on metal substrates or as an additivein a stronger matrix (see WO/11979). Polymer based bone cements withhydroxy apatite fillers is an established product. However, alltechniques involving elevated temperatures tend to alter themicrostructure of the hydroxyapatite, e.g. that the hydration water inthe hydroxyapatites leaves the structure.

[0013] Orthopedic components with hydroxyapatite based coatingsdeposited with various thermal spraying techniques, form a relativelylarge group of implants. Attempts have also been made to produce bio (orosseo-) compatible coatings of coral-like materials of calciumcarbonates. However, the limited mechanical properties of thesematerials set limitations to their use.

[0014] Calcium Aluminates

[0015] Another bioceramic is calcium aluminate, and its medicalapplications is described e.g. in S. F. Hulbert, F. A. Young, R. S.Mathews, J. J. Klawitter, C. D. Talbert. It is shown that tissues (bone,muscular, subcutaneous fat) to a large extent do not react when put incontact with pure calcium aluminate, i.e. no irritation, inflammations,or toxic reactions occur.

[0016] SE-463 493 discloses a chemically bound ceramic materialcomprising aluminates and silicates. The material is achieved through aproduction technique involving pre-compaction of the ceramic body. Inaddition, the ceramic material may comprise an inert phase of e.g.hydroxyapatite or oxides of titanium, zirconium, zinc and aluminium.

[0017] Calcium aluminate has been explored as a tooth filling material,e.g. the product Doxadent® produced by Doxa Certex AB, see e.g.PCT/SE99/01729, “Sätt att framställa en kemiskt bunden keramisk produkt,samt produkt”, Sep. 29, 1999.

SUMMARY OF THE INVENTION

[0018] The object of the invention is to provide a new method fordeposition of a chemically bonded ceramic surface coating, abiocompatible surface coating and a surface coated device, such that thedrawbacks of the prior art are overcome. This is achieved by the methodas defined in claim 1, the coating as defined in claim 18 and by thedevice as defined in claim 25.

[0019] One advantage with the method is that it is a low temperatureprocess, it can be used to deposit ceramic coatings on temperaturesensitive substrates.

[0020] Another advantage is that the coated device has improvedbiocompatibility, particularly in contact with bone.

[0021] Still another advantage is that the coating, again due to the lowtemperature deposition process, may be used as binder-material forbiocompatible materials such as hydroxyapatites and calcium carbonates,without altering their micro-structure or chemical composition, i.e. theexact biological properties is kept after deposition.

[0022] Furthermore, due to the simplicity of the method, deposition ofcoatings on selected sections of a substrate is possible. Also implantsmay be coated in a quick and simple way prior to the implant procedure.

[0023] Embodiments of the invention are defined in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The invention will be described in detail below with reference tothe drawings, in which:

[0025]FIG. 1 shows a schematic representation of the method according tothe present invention.

[0026]FIG. 2 shows a picture from optical profilometry (OP) measurementof a substrate surface after pretreatment step of blasting.

[0027]FIG. 3 is a diagram comparing the coating adhesion for pinspretreated in three different ways.

[0028]FIG. 4 is a diagram comparing the coating adhesion of the CAcoating prepared from a slurry comprising a water-reducing-agent with acoating prepared from a slurry not comprising a water-reducing-agent.

[0029]FIG. 5 is a diagram comparing the adhesion between coating andtitanium metal pretreated by wet alumina blasting and wet aluminablasting followed by CA blasting.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0030] The present invention is mainly concerned with coatings formedical devices, e.g. implants, laboratory equipment, tools for surgeryand the like. Commonly wanted bulk properties include high strength,elasticity, machinability, low leakage rates of alloy elements, etc. Therequirements on the surface region include biological properties, suchas toxicity, inflammation, rejection or other unwanted tissue reactions.Furthermore, the surface may exhibit different degrees of bioactivity,such as activation of cell growth, or controlled degradation, as well asbeing a carrier for active substances, e.g. pharmaceutical agents,growth factors, etc.

[0031] Throughout this application the term biocompatibility is used anumber of times implying certain properties on the material or surfacein question. However, is should be noted that biocompatibility is usedas a generic term for the different properties that are required ordesirable for materials that are to be in contact with biologicaltissue. Moreover, the material has to be used/prepared in the right wayand to be used in suitable applications.

[0032] Another frequently used term is osseo-compatible, which impliesthat a material has especially advantageous for use in contact with bonetissue. As presented above, some osseo-compatible materials even seemsto be capable of forming a direct bond with natural bone. Examples ofmaterials considered to be osseo-compatible are hydroxyapatite, andcoral-like materials of calcium carbonates.

[0033] The present invention includes a method for deposition, a coatingmaterial and products with a surface coating deposited according to themethod.

[0034] The material to be coated, hereafter referred to as thesubstrate, may be a ceramic, metallic or polymeric material. In apreferred embodiment of the invention the substrate is a metal acceptedin the field of medical implants, such as titanium, alloys of titanium,stainless steel or CoCr-alloys.

[0035] The present invention is preferably used to deposit ceramiccoatings on structures or implants intended for contact with biologicaltissues, and especially suitable in contact with bone tissue. Examplesof such structures or implants are, surface coated orthopedic implantse.g. hip- and knee joints, attachment elements (screws, nails, plates)for internal and external bone fixation and restoration of fractures.

[0036] The coating material of the invention is calcium aluminate eitheralone, or used as a binding phase with selected biocompatible and waterreducing agent additives.

[0037] The deposition is principally performed in three steps. Firstly,the surface of the substrate is pretreated, secondly the coating isdeposited as a slurry comprising calcium aluminate powder and a watersoluble solvent, and thirdly the deposited slurry is hardened. Thecalcium aluminate-water-slurry hardens by a chemical reaction, ahydration, and is thereby bonded to the surface of the substrate. Thehardening or curing of calcium aluminates is described in our co-pendingSwedish patent application SE-0104441-1, “Ceramic material and processfor manufacturing”, filed Dec. 27, 2001.

[0038] To achieve a coating with optimal properties, the following stepsare performed:

[0039] Pretreatment of the substrate surface

[0040] Preparation of the slurry, including addition of additives

[0041] Depositing the slurry on the substrate surface, and

[0042] Hardening of the slurry.

[0043] Each of these steps will now be presented more in detail (FIG.1).

[0044] Pretreatment of the Substrate Surface

[0045] It has been shown that a substrate surface pretreated with sandblasting in two steps result in optimal bonding between the coating andthe substrate surface. The first blasting step is preferably performedwith hard ceramic particles, generating a surface roughness with surfaceroughness values, R_(a)-values, in the range of 0.1 to 10.0 μm.

[0046] Most preferably the primary blasting is performed as awet-blasting, whereby the resulting surface has been shown to besubstantially free from blasting material. This is of great importanceas the substrate is to be used in biological applications.

[0047] The primary blasting may alternatively be another abrasiveprocess producing the same surface roughness, such as grinding with hardparticles or grit.

[0048] The second blasting is performed with calcium aluminate particlesas blasting medium. The second blasting should preferably be performedin such a way that calcium aluminate fragments are embedded into thesubstrate surface. The aim of this blasting is to achieve a betteranchoring of the coating on the substrate, and to provide seed pointsfor the following hydration of the calcium aluminate. This step may beachieved with dry blasting or other impingement method that producesrelatively high particle speeds.

[0049] To further enhance the bonding between the substrate and thecoating, the substrate may thereafter be pretreated with a watersolution containing an accelerator component that accelerates thehardening process of the calcium aluminate. Such accelerator componentsare well known in the field. Lithium chloride (LiCl) has been shown tobe an especially suitable accelerator. The purpose of the pretreatmentwith salt is to initiate the hydrating process in a controlled waydirectly on the substrate surface, whereby porosity, cracking etc. isavoided at the coating/substrate interface.

[0050] The calcium aluminate-water-slurry may be applied to thesubstrate surface either before or after the pretreated substrate hasdried.

[0051] Preparing the Slurry

[0052] As stated above, the slurry is comprised of a water-based solventand a powder, mainly comprised of ceramic components.

[0053] To achieve desired hardening characteristics and suitableproperties of the slurry, the water-based solvent comprises one or moreadditives. Preferably, the solvent is comprised of water, and one ormore components with dispersing, water-reducing, and wetting improvingproperties (hereafter referred to as water-reducing-agents). To achievedesired hardening times, the solvent often also comprises one or morecomponents that accelerates the hardening process (hereafter referred toas accelerator-agents).

[0054] One suitable accelerator-agent is LiCl, which is well known asaccelerator-agent in the concrete industry. To achieve suitablehardening speeds, the solvent may include from 0.01% to 1.0% by weight,preferably 0.05-0.1%. By altering the content of the accelerator-agentin the solvent, the hardening speed may be adjusted to be optimal for aspecific application.

[0055] Examples of other salts that may be used as accelerator- orretarding agents are: lithium hydroxide, lithium carbonate, lithiumsulfate, lithium nitrate, lithium citrate, calcium hydroxide, potassiumhydroxide, potassium carbonate, sodium hydroxide, sodium carbonate,sodium sulfate and sulfuric acid.

[0056] Generally, fast hardening is preferable when deposition of theslurry is performed by spraying, and slow hardening is preferable whendeposition is performed by dipping or a spin coating method.

[0057] Addition of water-reducing-agents (WRA) is needed to improve thewetting properties of the slurry, whereby the adhesion to the substrateis increased. It also leads to a more homogenous hydration process,whereby cracking; porosity etc in the substrate-coating interface isavoided.

[0058] Examples of such water-reducing-agents are water solutions ofpolycarboxylic polymers with PEG chains, and polyacrylic acids also withattached organic chains. Specific examples of water reducing productsare: Conpac 30 (Perstorp AB) Dispex A40 (Ciba GmbH, Schweiz), Glenium151 (Master Builders, Italy) SSP20 (Cementa AB, Sweden).

[0059] To achieve the desired effects, the solvent should include from0.05 to 5% by weight, preferably 0.1-1%. Preferably, the resultingslurry should have a water to cement ratio (w/c) in the range of 0.1 to0.9, preferably 0.1 to 0.4, to achieve a suitable viscosity.Alternatively, the solvent may be pure water, and the additives may beadded in dry state to the ceramic powder prior to the mixing with wateror to direct to the slurry.

[0060] In a basic form of the present invention, the mixture of ceramicpowder is only comprised of calcium aluminate. A number ofstoichiometries exist for the system. Commercially available powdersconsist mainly of CA or CA₂, where C stands for CaO and A for Al₂O₃,according to accepted cement chemistry notations. The phases C₁₂A₇ andCA₆ and C₃A have also been described in the literature. All phases areapplicable on the present invention. Such powders with sufficientquality are commercially available products, e.g. Secar and Ternal Whitefrom LaFarge Aluminates.

[0061] Binding phase systems based on hydrated calcium aluminate haveunique properties. In comparison to other water binding systems, forexample silicates, carbonates and sulphates of calcium, the aluminatesare characterised by high chemical resistance, high strength and arelatively rapid curing.

[0062] The high strength of calcium aluminate cements is due to the highabsorption capacity of hydrated water, which in turn results in a lowresidual water contents and low porosity. The high compaction alsoincreases the resistance to corrosion.

[0063] Generally, if a calcium aluminate powder is mixed with awater-based solution, a hardening process is initiated through achemical reaction between the calcium aluminate particles and water.More precisely, this hardening process is a hydration, whereby a newbinder phase comprised of calcium aluminate hydrate is formed. Thehydrates are formed by nucleation of crystalline hydrate phase from theliquid phase. The hydrate is thereafter transformed into differentcrystalline phases, with a rate depending on e.g. temperature andadditives. At room temperature the initially formed hydrate phase isCAH₁₀, where H═H₂O, and the most stable phase is C₃AH₆.

[0064] As disclosed in our co-pending Swedish patent application,SE-0104441Z-1, the coating may further comprise a material, e.g. forreducing the aluminum content in coating. As is proposed in SE-0104441-1calcium titanates, Ca/TiO₃, or other variants where Ti may besubstituted by Zr or Hf and Ca by Mg, Ca, Sr or Ba, in a perovskiticstructure, are preferred for this purpose, because they are biologicallysuitable and they do not substantially affect the mechanical propertiesof the material. I fact, all material compositions disclosed inSE-0104441-1 are applicable as coating materials in the presentinvention.

[0065] When needed, the ceramic powder is treated by a suitable millingprocess to obtain a uniform and well controlled size distribution. Onesuch type of milling process is presented in the example below, butother milling processes known in the field of ceramics could be used aslong as the desired result is reached.

[0066] More in general, the method according to the present inventionmay be used to produce coatings of any material with a binder-phase ofhydrated calcium aluminate, which may be applied to a substrate in theform of a slurry where after it hardens.

[0067] Depositing the Slurry on the Substrate

[0068] The slurry may be applied onto the substrate in a large number ofways, such as spray deposition, brush painting, spin-coating, dippingand the like.

[0069] To achieve a coating with optimal properties, in terms ofstrength, ductility etc, the coating should have a thickness in theorder of 0.1-200 μm, preferably less than 30 μm. Optimal properties arerelated to the possibility to produce an essentially defect-freecoating. As the size of defects normally is in the order of one to a fewμm, there is no space available for defects in sufficiently thincoatings, and the strength of the coating may approach the theoreticallimit for the material, which normally is about 100 times highercompared with the bulk strength of the material.

[0070] To prevent the slurry from curing excessively fast during thedeposition, the slurry may be kept at a low temperature, e.g. in therange 2 to 10° C., where after the temperature is raised to appropriatetemperatures during hardening as described in detail below.

[0071] Hardening of the Slurry

[0072] To achieve a coating with optimal mechanical properties, thehardening of the applied slurry has to be performed under specificconditions. As the hydration process consumes water, it is of greatimportance that the applied slurry is prevented from drying, i.e. thehardening has to be performed in wet (or at least moist) conditions.Therefore the hardening is preferably performed under controlledconditions with humidity of at least 90%, e.g. saturated oroversaturated vapor, or immersed in water.

[0073] Due to the very low thickness of the deposited layer of slurry,precautions have to be taken to prevent the slurry from falling of thesubstrate during hardening.

[0074] The hardening of the material may be performed in the temperaturerange from approximately 10° C. to 100° C. Above 100° C. the waterneeded for the hydration is evaporated and the slurry will dry.Preferably, the hardening is performed in the range from 20° C. to 70°C. If shorter hardening times and more complete hydration are desired,the more elevated temperatures may be used. The preferable hardeningconditions, in terms of temperature and humidity, may be achieved byauto-clavation.

ALTERNATIVE EMBODIMENTS OF THE INVENTION

[0075] In one embodiment, the calcium aluminate coating is used asbinder phase (carrier) for other biocompatible and/or osseo-compatiblematerials, whereby unique combinatory properties can be achieved.comprises adding particles or powder of one or more biocompatiblematerials. Suitable biocompatible materials comprises different types ofcalcium carbonates, calcium phosphates (preferably calcium salts ofortophosphoric acid) and apatites.

[0076] Addition of fragments or particles of apatites, such ashydroxyapatite or fluorapatite or carbonates-apatites, is especiallypreferred. Due to the low temperatures involved in the depositionprocess, these materials, being extremely temperature-sensitive, can becarried by the calcium aluminate coating, and their phase composition bepreserved.

[0077] Preferably, a powder of biocompatible materials is added to theceramic powder mixture when preparing the slurry, whereafter the coatingis applied onto the substrate and hardened as described above.

[0078] Such a calcium aluminate coating with improved biocompability mayprovide implants with osseo-compatible properties in applications wherecoatings of pure hydroxyapatite or the like are too weak.

[0079] The characteristics of the process and the coating material makeit possible to deposit coatings on devices that are sensitive to hightemperatures due to a low melting point, temperature expansion,hardening procedures and the like.

EXAMPLE

[0080] This non-limiting example describes one embodiment of the surfacecoating method according to the invention more in detail, and themechanical properties of these coatings.

[0081] In this example, round bars of pure medical grade titanium, ASTMGr.2, with a diameter of 6 mm, were used substrates. The titanium barswas pretreated with wet blasting using aluminum oxide grit with aparticle size of 100-120 mesh. The blasting was performed with apressure of 1 bar (air pressure). After blasting, the surface roughnessand morphology was characterized using Scanning Electron Microscopy(SEM) and optical profilometry (OP). The surface roughness was shown tobe in the range of R_(a)=0.6-0.7 μm after wet blasting, see FIG. 2.

[0082] To improve the bonding between the titanium and the coating, asecondary blasting of the metal surfaces was performed using calciumaluminate (CA) particles with a grit size between 0 and 22 μm (90%) at apressure of ˜10 bar (air pressure). The resulting surface morphology wasshown by a SEM picture, where 4 the dark areas represented CA enrichedareas on the titanium surface, whereas the light areas represented areaswith a smaller amount or none CA. This phenomenon is due to the loweratomic number for CA compared to titanium and was confirmed by elementalanalysis using Energy Dispersive Spectroscopy (EDS) of the dark andlight areas, respectively, of the CA blasted surface, CA-particles arebaked into the surface.

[0083] The CA-powder for the coatings, which in this example wascommercially available Ternal White, was treated by milling to obtain auniform and well controlled size distribution. The powder was milled iniso-propanol with chemically inert silicon nitride milling balls forthree days. This resulted in a powder with 99.6% of the grains having adiameter of less than 23 μm and most of the particles having a diameterof approximately 8 μm.

[0084] After milling, the milling balls were removed, and theiso-propanol evaporated. Thereafter, residual water and organiccontaminations were removed by burning of the dry powder for four hoursat 400° C.

[0085] The milled CA-powder was mixed with water, containing 0.01 gr ofLiCl in 100 gr of water. To improve the strength of the coatings, tofacilitate the spraying process, and to improve the wetting propertiesof the slurry, a water-reducing-agent (Conpac 30 from Perstorp AB), wasadded to the mixture resulting in a water to cement ratio ofapproximately 0.3. The slurry was mixed with a high speed rotatingdispersion mixer.

[0086] The CA slurry described above was sprayed on the pre-treatedtitanium metal substrates to a thickness of approximately 10-30 μm, andthen cured in saturated water vapor at 37° C. for 72 hours.

[0087] The adhesion strength between coating and titanium surface wastested with a torsion strength tester. All samples were prepared bycasting the sprayed titanium bars in a mould inside the test equipment.The test equipment is based on a collet clamped in a chuck, connected toa lever arm. The lever arm is in contact with a pushing rod, a straingauge sensor and a position indicator.

[0088] The adhesion test was performed by slowly bringing the lever armforward with the aid of the piston. The position of the piston and theforce of the lever on the piston were recorded, giving a measure of theforce and deformation distance required to wrench loose the round bar.

[0089]FIG. 3 compares the coating adhesion for pins pretreated in threedifferent ways: grinding with silicon carbide C, silicon carbide dryblasting B, and wet alumina blasting followed by CA blasting A.

[0090] In FIG. 4 the adhesion of the CA coating to the metal substrateis demonstrated for a coating prepared from a slurry comprising awater-reducing-agent D and for a coating prepared from a slurry notcomprising a water-reducing-agent E.

[0091]FIG. 5 compares the adhesion between coating and titanium metalpretreated by wet alumina blasting G and wet alumina blasting followedby CA blasting F.

[0092] To conclude, it is obvious from the example that the differenttechniques for pretreating the substrate surface, as well as theaddition of the water-reducing-agent, play a central role when a strongadhesion between the coating and the substrate surface is desired. Withsuitably selected pretreatments and additives, adhesion valuescomparable to the bulk strength of the cement are achieved.

1. Surface coating method for deposition of a chemically bonded ceramiccoating on a substrate, comprising the steps of: preparing a curablecoating slurry, comprising mixing calcium aluminate powder with waterand at least one water-reducing-agent, such that a water-to-cement ratioin the range of 0.1 to 0.9 is achieved. depositing a coating of theslurry on at least a section of the substrate surface, and hardening theslurry.
 2. Surface coating method according to claim 1, wherein the stepof preparing a curable coating slurry comprises adding a ternary oxideof perovskite structure according to the formula ABO₃, where O is oxygenand A and B are metals, or any mixture of such ternary oxides. 3.Surface coating method according to claim 2, wherein the ternary oxideis calcium titanate.
 4. Surface coating method according to any of theclaims 1 to 3, wherein the step of preparing a curable coating slurrycomprises adding particles or powder of one or more biocompatiblematerials.
 5. Surface coating method according to claim 4, wherein thebiocompatible material is a calcium carbonate.
 6. Surface coating methodaccording to claim 4, wherein the biocompatible material is a calciumphosphate, and preferably a calcium salt of ortophosphoric acid. 7.Surface coating method according to claim 4, wherein the biocompatiblematerial is an apatite.
 8. Surface coating method according to claim 7,wherein the apatite is selected from the group comprised of fluorapatiteor carbonates-apatites.
 9. Surface coating method according to claim 7,wherein the apatite is hydroxyapatite.
 10. Surface coating methodaccording to any of the claims 1 to 9, wherein the step of preparing acurable coating slurry comprises addition of a component whichaccelerates or retards the hardening process.
 11. Surface coating methodaccording to any of the claims 1 to 10, comprising the step of:pre-treating the substrate surface to a surface roughness in the rangeof R_(a) 0.1 to 10.0 μm before deposition of the slurry.
 12. Surfacecoating method according to claim 11, wherein the pretreatment isperformed by dry blasting with hard particles.
 13. Surface coatingmethod according to claim 11, wherein the pretreatment is performed bywet-blasting with hard particles.
 14. Surface coating method accordingto any of the claims 1 to 10, comprising the step of: embedding calciumaluminate fragments in the substrate surface.
 15. Surface coating methodaccording to claim 14, wherein the embedding is performed by blastingthe surface with calcium aluminate fragments or powder.
 16. Surfacecoating method according to any of the claims 1 to 15, comprising thestep of: pre-treating the substrate surface with an accelerator-agentfor accelerating the hardening process.
 17. Surface coating methodaccording to any of the claims 1 to 16, wherein the step of applying theslurry is performed by spraying, spin coating or dipping.
 18. Surfacecoating method according to any of the claims 1 to 17, wherein the stepof hardening is performed in water or in a environment with at least 90%relative humidity.
 19. Surface coating method according to any of theclaims 1 to 18, wherein the step of hardening comprises controlling thetemperature to be in the range of 10° C. to 200° C., preferably in therange 20° C. to 70° C.
 20. Surface coating method according to any ofthe claims 1 to 19, wherein the deposited coating has a thickness in theorder of 0.1-200 μm, and preferably is less than 20 μm.
 21. Method ofproducing a surface coated biocompatible device, comprising the stepsof: forming a substrate depositing a biocompatible surface coatingcovering least a section of the substrate surface using the surfacecoating method according to any of the claims 1 to
 20. 22. Biocompatiblesurface coating, wherein the binder phase in the coating substantiallyis comprised of calcium aluminate hydrate.
 23. Biocompatible surfacecoating according to claim 22, wherein it further comprises a ternaryoxide of perovskite structure described by the formula ABO₃, where O isoxygen and A and B are metals, or any mixture of such.
 24. Biocompatiblesurface coating according to claim 23, wherein the ternary oxide iscalcium titanate.
 25. Biocompatible surface coating according to any ofthe claims 22 to 24, wherein it further comprises particles or fragmentsof one or more biocompatible materials.
 26. Biocompatible surfacecoating according to any of the claim 25, wherein the biocompatiblematerial is a calcium carbonate.
 27. Biocompatible surface coatingaccording to any of the claim 25, wherein the biocompatible material isa calcium phosphate, and preferably a calcium salt of ortophosphoricacid.
 28. Biocompatible surface coating according to any of the claim25, wherein the biocompatible material is an apatite.
 29. Biocompatiblesurface coating according to any of the claim 28, wherein the apatite isselected from the group comprised of fluorapatite orcarbonates-apatites.
 30. Biocompatible surface coating according to anyof the claim 28, wherein the apatite is hydroxyapatite. 31.Biocompatible surface coating according to any of the claims 22 to 30,wherein it has a thickness in the order of 0.1-200 μm, and preferablyless than 20 μm.
 32. Biocompatible surface coating according to any ofthe claims 22 to 30, wherein it is deposited using the surface coatingmethod according to any of the claims 1 to
 20. 33. Surface coateddevice, comprising a substrate and a surface coating covering at least asection of the substrate surface, wherein the surface coating is abiocompatible surface coating according to any of the claims 22 to 32.34. Surface coated device according to claim 33, wherein the substrateis made of a metallic, ceramic or polymeric material, or any combinationthereof.
 35. Surface coated device according to claim 34, wherein thesubstrate is made of titanium or alloys thereof, stainless steel or aCoCr alloy, or any combination thereof.
 36. Surface coated deviceaccording to any of the claims 33 to 35, wherein it is a medical device.37. Surface coated device according to any of the claims 33 to 35,wherein it is a medical device for implantation.
 38. Surface coateddevice according to claims 36, wherein it is an artificial orthopedicdevice.
 39. Surface coated device according to claim 36, wherein it is aspinal implant.
 40. Surface coated device according to claim 36, whereinit is a joint implant.
 41. Surface coated device according to claim 36,wherein it is an attachment element.
 42. Surface coated device accordingto claim 36, wherein it is a bone nail.
 43. Surface coated deviceaccording to claim 36, wherein it is a bone screw.
 44. Surface coateddevice according to claim 36, wherein it is a bone reinforcement plate.